Thermal ink-jet print heads usually include a print die, e.g., formed on a substrate of silicon or the like using semi-conductor processing methods, such as photolithography or the like. Print dies normally include resistors and an ink delivery channel that delivers the ink to the resistors so that the ink covers the resistors. Electrical signals are sent to the resistors for energizing the resistors. An energized resistor rapidly heats the ink that covers it, causing the ink to vaporize and be ejected through an orifice aligned with the resistor so as to print a dot of ink on a recording medium, such as a sheet of paper.
A portion of the heat dissipated by the resistors that does not go into vaporizing the ink is conducted through the substrate and is subsequently convected away by the ink flowing through the ink delivery channel. However, the print die can still overheat, causing the print head to stop printing.